1. Field of the Invention
The present invention relates to a liquid residual quantity detecting method for detecting a residual quantity of a liquid, such as a liquid fuel for use in a fuel cell for driving an image pickup apparatus (camera), a portable apparatus, or a like electronic apparatus, a liquid residual quantity detecting device for executing the method, a program for implementing the method, and a storage medium storing the program.
2. Description of the Related Art
Recently, there have been proposed various kinds of image pickup apparatuses and portable apparatuses, as electronic apparatuses using a fuel cell as a power supply driving the same.
As fuel cells for electronic apparatuses, there has been proposed a fuel cell that generates electric power by directly supplying a liquid organic fuel, such as methanol, to its anode (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-056857).
The proposed fuel cell is simple in construction since it does not necessitate a reformer for reforming the liquid organic fuel, such as methanol, into a hydrogen-rich reformed gas, and is therefore regarded as a promising power supply for portable apparatuses.
Now, a brief description will be given of the principle of power generation by the fuel cell of the above-mentioned type. The fuel cell (DMFC) is usually operated by supplying air to its cathode and supplying an organic fuel to its anode, which causes a chemical reaction expressed by the following formula (1):CH3OH+H2O→CO2+6H++6e−  (1)
Then, protons (H+) generated on the anode side move to the cathode side through a solid polymer membrane as electrolyte to react with oxygen atoms from the air as expressed by the following formula (2):O2+4H++4e−→2H2O  (2)
Carbon dioxide and water are generated upon generation of electric power.
The fuel cell is advantageous not only in the capability of generating electric power simply by supplying fuel and an oxidizer but also in the capability of continuously generating electric power by refilling fuel. Compared with a secondary battery which takes several hours to be charged, it can be said that the fuel cell is restored almost instantaneously. In addition, the fuel cell has a big advantage in its suitability for driving portable apparatuses with small power consumption.
However, since the fuel cell uses liquid fuel which moves depending on the position of a portable apparatus in which it is used, there is a demand for means for correctly detecting the residual quantity of the fuel.
Conventionally, there has been proposed a fuel storage system configured to store an increased amount of liquid fuel for fuel cells within a portable apparatus (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-100376).
Further, there has conventionally been proposed a fuel gauge structure for fuel gauges of automotive vehicles, which is capable of informing a user that the residual quantity of fuel cannot be correctly indicated due to inclination of a vehicle body (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H09-257550).
Furthermore, there has conventionally been proposed a fuel residual quantity display device for vehicles, which is hardly affected by the position of the vehicle but is capable of correctly indicating the residual quantity of fuel even when the vehicle is not in a horizontal position, i.e. is in a tilted position (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H11-190655).
However, the above-described conventional techniques have the following drawbacks:
The fuel storage system disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-100376 uses a fuel cell unit for portable apparatuses, but has been proposed to provide a novel layout of a fuel tank, and therefore the publication does not describe at all the detection of the residual quantity of fuel, warning of the residual quantity of fuel, or replacement of fuel cells.
In the fuel gauge structure disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H09-257550, the residual quantity of fuel is constantly displayed whether it may be correct or incorrect. Therefore, it is difficult to determine at a glance whether or not the indication of the fuel residual quantity is correct.
Further, the fuel residual quantity display device for vehicles disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H11-190655 is capable of correctly indicating the residual quantity of fuel even when the vehicle is tilted, but this device needs not only a detecting means for detecting tilt of the vehicle, but also other various means, such as a storage means, a holding means, and a control means, which inevitably increases manufacturing costs, increases the size, and makes the device complicated in construction.